1. Field of the Invention
The present invention relates to the technical field of rotating electric machines. It refers to an elastic insulating material element for wedging a winding, in particular the stator winding, of an electric machine in the slots provided for this purpose in a laminated body.
Such an insulating material element is known, for example, from the publication U.S. Pat. No. 3,949,255 or U.S. Pat. No. 4,200,816.
2. Description of Background
Elastic insulating material elements are employed, in particular in the stators of rotating electric machines, for elastic fastening (wedging) of the stator winding in the slots of the laminated body. The stator windings are, as a rule, insulated conductor bundles of rectangular cross section which are inserted with slight play into slots of the stator body. In order to ensure a firm fit of the winding in the slot, the wedging must withstand stresses due to the intrinsic mass of the winding and to electromagnetic forces occurring during operation and in the event of a short circuit, in such a way that it does not become possible for the winding to be loosened and to vibrate.
Conventional slot wedges, in particular for relatively small machine units, consist of an insulating material which is worked or machined in the form of a prism. As a rule, glass-fiber reinforced epoxy resin is used as insulating material (see, for example, U.S. Pat. No. 4,200,818). With the aid of a plastically elastic intermediate layer (fleece, felt), these wedges are adhesively bonded axially into the slots of the toothed tips of the lamination stack and partly, in an impregnating process, to the winding and the lamination body. Another conventional wedge design is based on the action of double wedges. Two flat wedges located one above the other are pushed into the wedge slots, the prestressing force being built up by one flat wedge being driven axially (see, for example, U.S. Pat. No. 3,949,255).
A disadvantage of both forms of wedge is that the wedge design is inherently rigid and inflexible. The prestressing force is undefined. Thermal expansions of the slot packing result, due to rigid wedging, in an enormous increase in the pressure forces exerted on the slot packing, and this may lead to a pronounced settling of the slot packing, with the resulting undesirable loosening of the winding.
Wedging with the aid of plastic corrugated springs (U.S. Pat. No. 3,949,255) eliminates the disadvantage of inelastic wedging. For this purpose, elastic corrugated springs are inserted between a rigid wedge and a winding (or between two rigid wedges). The necessary prestressing force is achieved by the defined compression of the corrugated spring. Shrinkage of the slot packing due to settling processes is compensated by the respringing of the corrugated spring. Use of elastic wedges is another solution for achieving elastic wedging. By means of appropriately thin wedges or centrally cut-out wedges (convex/concave wedges), the flexibility of the wedges is increased and the prestressing forces are reduced. With this solution, too, settling processes in the slot packing can be compensated to some extent.
In both elastic wedging methods, maintaining the minimum prestressing force permanently is ensured only when the elastic plastic elements also preserve their elastic properties completely. It is known, however, that all reinforced plastics tend to yield or creep under constant bending stress and, in particular, increased temperatures. As complicated tests have shown, considerable yield is already to be expected at normal operating temperatures, even when fiber reinforced plastics with heat-resistant binders are used. In the event of operating faults in which temperatures are increased even further for a short time, yield of this kind may become critical, so that there is the possibility of loosening of the winding.